I agree with the thrust of what Jeanette and Ken said but I've found that sometime you just have to cut your losses. Sometimes it's because the person is a lost cause but mostly just because they want to dominate your time while others are getting impatient and walking away. It's especially disappointing when it's kid walking away dissatisfied.
I think my least favourite is the 'how much does that cost' or 'what should I buy' when I have twigged that they will never actually buy a scope or get into the hobby. Too often I've told people that you can get a decent scope for $300-400 only for them to reply to the effect 'that much?' or 'wow, I didn't know it was that expensive'.
I feel like telling them to take up golf.
